Stationary ultrasonic horns and anvils are commonly used for bonding a member to a moving web of an inelastic material. Problems arise when the raised dot pattern of the anvil is brought into contact with a moving web of elastomeric material. The web tends to ripple and become torn when passing over the raised dot pattern of the anvil during the bonding process. This problem cannot be remedied by using a smooth anvil having no dot pattern, even if a vacuum is associated with the anvil, because the raised dot patterns are required for bonding. Thermal bonding is inadequate because it does not sufficently penetrate the laminar structure of some elastomeric nonwoven fibrous webs. Thermal bonding tends to burn the surfaces of the laminar facing layers.
Vacuum mechanisms have been used in the prior art to hold down various elastic and inelastic materials. The U.S. Pat. Nos. 4,081,301 to Buell, issued Mar. 28, 1987; 4,022,366 to Rooney, issued May 10, 1977; and 3,853,662 to Yazawa et al, issued Dec. 10, 1974 each disclose a vacuum mechanism for holding down a material to a belt. The Buell patent discloses a method and apparatus for continuously attaching discrete, stretched elastic strands to predetermined isolated portions of disposable absorbent products. The vacuum hold down belt supports and carries a continuous web of disposable diapers. A suction box is attached to the underside of the belt. Vacuum in the box holds the web over the perforated belt and thereby provide sufficient resistance to slippage.
The Rooney patent discloses a belt made of an air pervious material, preferably a woven fabric.
The Yazawa et al patent discloses a process for laminating uniaxially stretched layers of film as warps or wefts utilizing a vacuum mechanism for sucking the layer of material onto a belt by negative pressure exerted from below the belt.
None of the aforementioned patents address the problem of continuously ultrasonically bonding two web materials into a laminate as the web materials are carried on a continuously moving support nor the specific problem of the material being ripped or torn by movement of the moving web against an anvil during bonding.
The U.S. Pat. No. 4,419,160 to Wang et al, issued Dec. 6, 1983, discloses a method and apparatus for dying nonwoven fabric. The Wang et al patent discloses an ultrasonically bondable web of random loose fibers that are held on an endless conveyor screen such as wire, by a vacuum system. The material is discharged from the end of the screen and advanced between overlying horns and underlying anvils of an ultrasonic welding machine. A vacuum is not applied at the point of ultrasonic bonding and the anvil includes various projections which could rip or tear an elastic web material.
The U.S. Pat. No. 3,575,752 to Carpenter, issued Apr. 20, 1971, discloses a metallic screen placed over an anvil surface upon which a nonwoven fabric is bonded. A drive drum propels an endless belt which is in the form of a metallic screen. A nonwoven fabric is supported on the belt to a bonding station under a reciprocating ultrasonic horn. A rigid anvil is disposed directly under the horn and under the belt. The screen belt functions in conjunction with the anvil as a mesh pattern anvil surface upon which the horn works against the intervening workpiece. There is no vacuum applied under the wire mesh. Accordingly, a laminate traveling over the anvil would not be held against the wire screen. There would be a potential for tearing and ripping of the web, as well as loss of contact between the horn and wire screen. There is further no disclosure of a specific structure of a wire screen which can act solely as an anvil in cooperation with the horn to perfect an ultrasonic bonding operation.
The U.S. Pat. No. 3,640,786 to Carpenter, issued Feb. 8, 1972, discloses a method of making pile fabrics wherein thermoplastic pole yarn is fusion bonded to a thermoplastic backing by means of sonic energy. The Carpenter '786 patent discloses a backing member supported in advance by a feed mechanism including an endless belt preferably in the form of a screen that is entrained about a drive drum disposed below an ultrasonic horn. The belt, in combination with the drive drum which backs up the belt serves to advance the backing member to the bonding line and also serves as an anvil member against which the work is compressed by the horn during bonding. No vacuum mechanism is disclosed for retaining two laminate layers on the moving belt, nor is there any direction to the problem of elastomeric fibrous web materials being carried over projections of a anvil.
Plastic web is very difficult to control as the web stretches before it moves. Prior art methods discussed above which do not include a vacuum mechanism cannot maintain the laminated webs at a constant tension during a bonding process. No prior art patents relate to a continuously moving web and a stationary horn for effectively perfecting an ultrasonic bond. Further, the prior art patents do not address the problem of providing a moving forming screen having a construction whereby the screen solely provides an anvil for the ultrasonic bonding process.
The present invention addresses the above discussed problems by providing a vacuum drawn forming screen for movably supporting and carrying an elastic fibrous web while a member is being ultrasonically bonded thereto.